A static pressure type non-contact gas seal has been known as a conventional mechanical seal, including a rotary sealing ring that is fixed to a rotating shaft; a stationary sealing ring that is held by means of a pair of O-rings in a seal case through which the rotating shaft passes, so as to move in an axial direction thereof; and a spring that is interposed between the stationary sealing ring and the seal case so as to push the stationary sealing ring against the rotary sealing ring, wherein a communicating space sealed by the pair of O-rings is formed between the seal case and the stationary sealing ring, and a seal gas ejecting passage is formed as a series of passages that communicate with each other through the communicating space in the seal case and the stationary sealing ring, and is open between the sealing end faces serving as the opposite end faces of the both sealing rings, thereby so as to maintain the sealing end faces in proper non-contact state by introducing the seal gas under a predetermined pressure between the sealing end faces through the seal gas ejecting passage (for example, see Patent Document 1).
Meantime, when the seal conditions or the structural conditions taken into account in the above-mentioned static pressure type non-contact gas seal, it may be preferable or may be inevitable to hold the O-rings engaging with the periphery of the stationary sealing ring, as the case may be.
Patent Document 1: WO 99/27281 (FIG. 8)
However, the O-rings, being held engaging with the stationary sealing ring, slide in press contact with the periphery of the seal case in accordance with the movement of the stationary sealing ring in the axial direction thereof, and consequently cause the following problems.
That is, since the seal case is made of a metal having an excellent strength in view of the function, the O-rings do not slide smoothly following the movement of the stationary sealing ring owing to the high contact resistance between the O-rings and the seal case. As a result, the stationary sealing ring, which does not move smoothly in the axial direction thereof, deteriorates its own following ness so as to result in failure of an effective sealing function by the mechanical seal. Particularly, when the supply of the seal gas stops in the above-mentioned static pressure type non-contact gas seal, it is concerned that the stationary sealing ring, which does not smoothly move toward the rotary sealing ring, may intensively collide against the rotary sealing ring, so that the sealing end faces may be damaged by some possibility. To the contrary, when the supply of the seal gas stops, the stationary sealing ring does not move, but may form a gap between the sealing end faces. In this case, it is concerned that the resumed supply of the seal gas does not generate a proper static pressure between the sealing end faces but leads to the lost sealing function.
There occurs, similarly, such a problem in an end face contact type mechanical seal, in which the both sealing rings are slidably rotated relative to each other to obtain a sealing function, and also in a dynamic pressure type non-contact type mechanical seal which is configured to maintain the sealing end faces in non-contact state by dynamic pressure generated therebetween.